Carbohydrates Flashcards
What does a plant do when needs more glucose/ energy?
Breaks down / hydrolisis starch to release glucose for respiration
When testing for sugar what does it mean if:
A) it turns blue first time testing
B) if turns green, yellow, orange, brick red second time
2 marks
A) there are no reducing sugars present but possibility that non reducing sugar is present
B) it is non reducing
Why would you connect a glycosidic bond at the top?
As the OH needed for the reaction is at top rather than bottom. So can’t connect next to each other.
How do you separate polysaccharide into monosaccharides?
(In diagrams)
Split glycosidic bond and add H on either side.
A precipitate is produced in a positive result for reducing sugar in a Benedict’s test.
A precipitate is solid matter suspended in solution.
A student carried out the Benedict’s test. Suggest a method, other than using a colorimeter, that this student could use to measure the quantity of reducing sugar in a solution.
2 marks
- Filter and dry (the precipitate)
Accept: correct reference to evaporation after filtration
——————-
- Find mass / weight
Lactulose is a disaccharide formed from one molecule of galactose and one molecule of fructose.
Other than both being disaccharides, give one similarity and one difference between the structures of lactulose and lactose.
2 marks
Similarity
Both contain a glycosidic bond/ galactose
. Ignore reference to hydrolysis and / or condensation
——————————-
Difference
Lactulose contains fructose, whereas lactose contains glucose
. Ignore alpha / beta prefix for glucose
. Difference must be stated not implied
During early pregnancy, the glycogen in the cells lining the uterus is an important energy source for the embryo.
Suggest how glycogen acts as a source of energy.
Do not include transport across membranes in your answer.
2 marks
- Hydrolysed ( to glucose )
- Glucose used in respiration
- Ignore “broken down”
- “Energy produced” disqualifies mp 2
In mammals, in the early stages of pregnancy, a developing embryo exchanges substances with its mother via cells in the lining of the uterus, At this stage, there is a high concentration of glycogen in cells lining the uterus.
Describe structure of glycogen
2 marks
- Polysaccharide of alpha glucose
Or
polymer of alpha glucose
2.
(Joined by) glycosidic bonds
Or
Branched structure
A student wanted to produce a dilution series of a maltose solution so he could plot a calibration curve. He had a stock solution of maltose of concentration 0.6 mol dm-3 and distilled water. He made a series of dilutions from 0.1 to 0.6 mol dm-3.
Complete the table below
First row
A) Concentration units?
. Volume 0.6moldm3 maltose solution cm3
B) what is third row box name and units
Second row
A) conc of maltose?
. 5moldm3 volume maltose
. 10 vol of ?
(2 marks)
First row
A) mol dm-3
B) volume of water / cm3
Second row
A) 0.2
. ? =vol of water
Starch molecules and cellulose molecules have different functions in plant cells. Each molecule is adapted for its function.
Explain one way in which starch molecules are adapted for their function in plant cells.
2 marks
- Insoluble;
- Doesn’t affect water potential
Or
- Helical
. Accept form spirals
- Compact
Or
- Large molecules
- Cannot leave cell
Describe the chemical reactions involved in the conversion of polymers to monomers and monomers to polymers.
Give two named examples of polymers and their associated monomers to illustrate answer.
5 marks
A condensation reaction joins monomers together and forms a (chemical) bond and releases water;
A hydrolysis reaction breaks a (chemical) bond between monomers and uses water;
Examples include:
Amino acid to protein
Alpha glucose to starch/glycogen
Beta glucose to cellulose
Nucleotide to DNA/RNA
A second suitable example of polymers and the monomers from which they are made;
Reference to a correct bond within a named polymer ( glycosidic)
Name three disaccharides and for each one, state monosaccharide constitutes?
Maltose - 2 glucose molecules
Sucrose - glucose and fructose
Lactose - glucose and galactose
Is ATP made/produced during photosynthesis and respiration?
Yes
Explain how cellulose molecules are adapted for their functions in plant cells. (3 marks)
(1) Long and straight chains;
(1) Become linked together by many hydrogen bonds to form fibrils;
(1) Provide strength (to cell wall).
Glycogen and cellulose are both carbohydrates.
Describe two differences between the structure of a cellulose molecule and a glycogen molecule.
2 marks
- Cellulose is made up of B-glucose (monomers) and glycogen is
made up of a-glucose (monomers);
——————————
- Cellulose molecule has straight chain and glycogen is branched;
————————
- Cellulose molecule has straight chain and glycogen is coiled;
———————-
- glycogen has 1,4- and 1,6- glycosidic bonds and cellulose has only 1,4- glycosidic bonds;
. Ignore ref. to H bonds / microfibrils
Starch is a carbohydrate often stored in plant cells.
Describe and explain two features of starch that make it a good storage molecule.
2 marks
Any two from:
1. Insoluble (in water), so doesn’t affect water potential;
————
- Branched / coiled / (a-)helix, so makes molecule compact;
OR
Branched / coiled / (a-)helix so can fit many (molecules) in small area:
—————-
- Polymer of (a-)glucose so provides glucose for respiration;
————————
- Branched / more ends for fast breakdown / enzyme action;
—————-
- Large (molecule), so can’t cross the cell membrane
————
Require feature and explanation for 1 mark
- Accept symbol of WP
- Accept insoluble so doesn’t affect osmosis
- Do not allow ref to ‘doesn’t affect water leaving cells
- Ignore ‘surface area’
- Accept ‘branched so glucose readily released’
